Traumatic brain injury (TBI) alters the lives of many civilians and those involved in armed conflicts. Sequalae of TBI include depression in up to 30% of cases. Appearance of depression after TBI impairs recovery and results in sub-optimal re-integration into society. Treatment of post TBI depression relies on oral medications, whose efficacy and side effect profile is sub-optimal. Exercise training is effective in spontaneous depression as a stand-alone treatment and in conjunction with oral medications, and this may represent an alternative treatment option in the TBI population. Further, the pathophysiology of depression after TBI has yet to be examined with the full scientific rigor required. This project proposes to use exercise training of moderate intensity as a treatment for depression after TBI, while measuring biological markers as a way to investigate efficacy and provide insight into the pathophysiology. This mentored career development award would allow further training and education of the candidate in exercise training, depression, sophisticated imaging techniques and the analysis of such data. The candidate's career goal is to be an expert in depression after TBI, thereby improving outcome through understanding the pathophysiology and seeking population specific treatments. UT Southwestern is one of the leading academic medical centers in the United States, with a proven record of scientific excellence. Home to four Nobel Laureates, it is also the home institution of world renowned experts in depression and traumatic brain injury. Its major teaching institution, Parkland Memorial Hospital, maintains a Level One trauma designation, caring for 3000 trauma patients annually. Exercise training will take place at the Institute for Exercise and Environmental Medicine.